1. Field of the Invention
The invention relates to the field of ski-supported vehicles. More particularly, the invention relates to snowmobiles equipped with wheels that will allow the snowmobile to travel readily over surfaces not covered with snow or ice.
2. Description of the Prior Art
Snowmobiles are vehicles that are constructed to travel across snow and ice. As is generally known, the snowmobile is driven by an endless drive track arranged at the rear end of the underside of the snowmobile. The front end of the snowmobile is supported and rides along two skis, which glide across the surface of the snow or ice. The skis typically have a carbide runner that runs along a portion of the bottom surface of the ski, to help keep the snowmobile traveling along a smooth track.
A disadvantage of snowmobiles is that the skis don""t readily glide across gravel, hardtop, or other non-snow surfaces. This makes it difficult, if not impossible, to steer a snowmobile because the skis do not respond properly to the steering operations initiated at the handlebars. Quite often, the snowmobile needs to be dragged or pushed in driveways and across roadways, etc. Furthermore, when a snowmobile is driven or dragged across a non-snow surface, the carbide runners on the skis are subject to excessive wear and must be replaced more frequently, depending on how often a snowmobile travels across a non-snow surface. This inability to steer snowmobiles on surfaces other than snow and ice makes it difficult for people to maneuver their snowmobiles across roadways, driveways, onto ferries, etc.
In recent years, the sport of snowmobiling has changed evolved from one of traveling relatively short distances over trails close to home to one of weekend-long or longer cross-country trips. Previously, for example, a snowmobile operator would fill the gasoline tank of the snowmobile in his or her backyard, transport the snowmobile to a trail site or depart directly from the backyard for an afternoon or day of travel over snowmobile club trails, and then return home. Nowadays, people are traveling great distances across country on snowmobiles that involve two-or three-day tours or even such mammoth tours as from Alaska to Maine.
This development of the sport of snowmobiling into extended trips means that snowmobiles must now be refilled with gasoline and maintained while they are out traveling across open country. Thus, where in the past the tank on the snowmobile was filled at home or at the point of departure before a daylong excursion, snowmobiles now need to be refilled while out traveling. This means that the snowmobile must be driven to a service station, typically by traveling some distance along a road surface other than snow or ice. Also, now that such lengthy trips are being undertaken with snowmobiles, the presence of snow along the entire route is not guaranteed, and consequently, snowmobiles are being required more and more frequently to travel some distance across surfaces other than snow or ice. Before, when a snowmobile needed to be dragged or pushed only a short distance across a roadway or driveway, or up a ramp onto a ferry, it was possible for a person to do it alone or with the assistance of a traveling companion. Now, however, with the need to travel several miles along a roadway to get to a filling station, the inability to steer a snowmobile has become a major obstacle in the logistics and the enjoyment of the sport.
Efforts to make snowmobiles mobile on gravel or other surfaces have been undertaken over the years. Prior art includes conversion kits to replace the skis with wheels. These conversion kits were intended to replace the skis on a semi-permanent basis, that is, to convert a snowmobile into a wheeled vehicle for an extended period of time. Such conversion kits typically require that the ski be removed in order to mount the wheels, or, if the ski does remain attached to the vehicle, a longer kingpin must be used to mount the wheels. Thus, each time the wheels are mounted or removed, the kingpin must be replaced with the longer or shorter one, respectively. Both methods of converting the snowmobile to a wheeled vehicle involve a fair amount of work. Thus, such conversion kits are not generally an acceptable solution to the problem of having to change in relatively quick succession back and forth between a vehicle that rides on skis and one that rides on wheels, as happens when traveling over gravel or hardtop or other surface other than snow or ice to fill the gas tank or to load onto a ferry.
What is needed, therefore, is a means for quickly converting a vehicle from one gliding on skis to one rolling on wheels and back. What is further needed is such a means that will not impair the steerability of the vehicle. What is yet further needed is such a means that can be implemented easily, without requiring great physical strength, and without requiring the use of tools.
An object of the present invention is to provide a combination ski-wheel unit that will allow one to convert a ski-supported vehicle quickly and easily to a wheeled vehicle and back to a ski-supported vehicle, without requiring the use of tools. Another object of the present invention is to provide such a unit that will maintain the steerability of the vehicle, whether on skis or on wheels. A further object is to provide such a unit that, once installed, can be easily deployed without requiring great physical strength. Still another object is to provide a wheel kit with deployable wheels that can be retrofitted onto any conventional snowmobile ski.
The objects are achieved by providing a road wheel unit that is semi-permanently installed on the ski of a conventional snowmobile so as to provide a set of wheels that are easily deployable or retractable as the conditions require. The road wheel unit includes a kingpin to replace the conventional kingpin to which the ski spindle attaches, a wheel mounting bracket mounted on each side of the kingpin, and a movable frame that is mounted onto the wheel mounting bracket, outside the ski. In a retracted position, i.e. the standard snowmobile mode of operation, the wheels are carried alongside the ski, raised above the gliding surface of the ski. In a deployed position, the wheels are lowered, so that the weight of the machine is supported by the wheels. The wheels in this deployed position hold the ski above the rolling surface of the wheels, and allow the snowmobile to ride on wheels and the conventional endless track at the rear end. In the latter mode, the snowmobile remains readily steerable with the handlebars and the carbide runners on the ski surfaces are not subject to excessive wear. If desired, the wheels can simply be unscrewed from the wheel mounting bracket, leaving the frame, wheel mounting bracket and modified kingpin permanently on the vehicle.
In one embodiment of the wheel unit, the movable frame has a crossbar and a yoke that depends from the crossbar into the inner contour of the ski. The movable frame can be locked in two positions, a retracted position and a deployed position. To deploy the wheel unit, a person lifts the ski by the handle that is typically provided at the front end of the ski, grabs hold of the crossbar and slightly lifts and slides it forward toward the front end of the ski until the yoke latches with a latching mechanism provided on the inner bottom surface of the ski. The two wheels, one on each side of the ski, are thereby lowered and secured in the deployed position. The snowmobile can now be driven across gravel and hardtop surfaces without losing its ability to be steered with the handlebars.
To retract the wheels, the procedure is reversed. A person lifts the ski until the weight of the snowmobile is off the wheels, grabs the crossbar and slides it toward the rear end of the ski until it is secured in a retracted position. The wheels are now secured in a raised or retracted position in which the lowest point of the wheels is above the gliding surface of the ski, allowing the snowmobile to glide fully on the skis.
It is within the scope of this invention to provide a wheel unit for ski-mounted vehicles that can be actuated in a variety of ways. What was described above is a simple mechanical actuation. It is, of course, possible to provide any number of automated or power-assisted means of deploying and retracting the wheels. In one embodiment, the movable frame is spring-biased toward the retracted position, so that, when the snowmobile weight is lifted from the ski, the wheels will automatically spring back to a retracted position. Other means for actuating the deployment and retraction of the wheel unit according to the invention include such means as a pivot arm or linkage driven by an electric motor, an electro-magnetic means in which magnets are selectively magnetized to draw the frame to a deployed or retracted position, or hydraulic or pneumatic means. In a Preferred Embodiment, a small electric motor is placed within the inner contour of the ski and wired to a thumb switch on the handlebar of the snowmobile. The motor drives a shaft that is connected to an arm that is pivotably linked to the frame. When the shaft extends, the frame is pushed to a deployed position, thereby lowering the wheels to an operable level, and when the shaft retracts, it pulls the frame to a retracted position, thereby lifting the wheels above the level of the gliding surface of the ski. An indicator, for example, a warning light is arranged on the dashboard or on the handlebar, to alert the operator when the wheel unit is deployed.
Although it is desirable that snowmobiles be sold equipped with wheel units according to the present invention, a wheel kit is provided to retrofit any of the conventional snowmobiles already available. The ski itself need not be modified. The original kingpin is replaced with the modified kingpin according to the invention, to which the wheel unit is attached. Depending on the type of wheel unit actuation means chosen, manual, electric, or other, an actuation means, a switch and/or an indicator light may also be retrofitted on the snowmobile.
With the wheel unit of the present invention, the wheels are semi-permanently mounted on the ski. Depending on the particular travel conditions, the wheels can be deployed, so that the snowmobile becomes a wheeled vehicle, or retracted, so that the wheels are carried along side the ski in a raised position, above the gliding surface of the ski.